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Draft Soils FS Report Memorandum -5- 17 April 1992 <br /> DDRW, Sharpe <br /> C. Number of Soil Borings. The number of soil borings in each WMU was not <br /> presented. It is unknown whether the number of soil borings was based on <br /> statistics, the size of the WMU or on some other criteria. In addition, it is <br /> unknown why some WMUs did not have any soils boring installed as part of the <br /> WMU investigation. The rationale for the number of borings, as well as why <br /> some WMUs were not investigated, should have been summarized in the Draft Soils <br /> FS Report. <br /> d. Location of Soil Borings. Some of the soil borings installed to investigate a <br /> WMU were installed too far away from the source. Samples collected from these <br /> borings would tend to have lower concentrations of contaminants and will not <br /> yield data which can be used for remediation of the source area. For example, <br /> S#1 was installed approximately 200 feet away from the building in which <br /> pesticides were mixed and stored (Building T-47) . Soil borings installed this <br /> far from a potential source are not representative and therefore, not <br /> acceptable as the only data for that WMU or UST. In general , the soil borings <br /> should have been installed in the WMU, if possible, or immediately down <br /> gradient of the WMU. <br /> e. Location of Down Gradient Monitor Wells. Many of the monitor wells used to <br /> determine potential ground water impacts are several hundred feet down gradient <br /> from the WMUs and USTs. Wells placed these distances from the WMU or UST are <br /> inadequate as detection monitor wells. For example, MW-437 and MW-454 used to <br /> determine potential ground water impacts from waste disposal at Building 839 <br /> (paint stripping operations) are approximately 700 and 800 feet down gradient <br /> from the source area. New monitor wells, immediately down gradient of the WMU, <br /> need to be installed to determine if ground water has been impacted. <br /> f. Background Contaminant Concentrations. Background concentrations of <br /> contaminants were not summarized in the Draft Soils FS Report. It is unknown <br /> how or if background concentrations for each contaminant of concern were <br /> determined. Background concentrations for VOCs, semi-VOCs, petroleum <br /> hydrocarbons and pesticides can be assumed to be non-detect (ND) as these types <br /> of contaminants are not naturally occurring in the unsaturated zone. However, <br /> background concentrations for most heavy metals are unknown or are not <br /> reported. Background concentrations may need to be determined because cleanup <br /> levels would be NO if technically and economically feasible, unless the metal <br /> is naturally occurring. <br /> g. Screening Pesticides in Soils. An Organic Vapor Analyzer (OVA) and <br /> Photoionization Detector (PID) were used to detect the presence of pesticides <br /> in soil samples. Use of an OVA and PID are inappropriate because not all <br /> pesticides are volatile and therefore, these instruments would not detect their <br /> presence. An amino assay should have been used to screen for pesticides in <br /> soils samples. This colorometric method of screening is used to detect high <br /> concentrations of pesticides. <br /> h. Analysis for Pesticides. Analysis for pesticides are assumed to have been <br /> performed using Method 8080 which detects the presence of organochlorine <br /> pesticides and PCBs. However, there are several different types of pesticides: <br /> chlorinated herbicides (Method 615) , organophosphorus pesticides (Method 614 or <br /> 622) , organohalide pesticides (Method 617) , triazine pesticides (Method 619) , <br />